Static-dissipative coating technology

ABSTRACT

The invention provides a glass sheet or another transparent substrate on which there is provided a static-dissipative coating. The static-dissipative coating includes a film comprising titania. The film comprising titania preferably is exposed so as to define an outermost face of the static-dissipative coating. The static-dissipative coating is characterized by an indoor dust collection factor of less than 0.145.

RELATED APPLICATIONS

This application is a U.S. utility application claiming priority to U.S.provisional application No. 62/423,276, filed Nov. 17, 2016, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to coatings for glass and othersubstrates. More particularly, this invention relates to low-maintenancethin film coatings.

BACKGROUND OF THE INVENTION

Various types of photocatalytic coatings are known. Self-cleaningcoatings based on TiO₂, for example, have been studied widely andreported on in the scientific literature. Many past efforts have soughtto maximize the photocatalytic properties of the coating, in some caseswith the goal of providing a self-cleaning window. In such cases, highlevels of photoactivity are desired.

Contrary to the goal of such research efforts, it can be advantageous toprovide low-maintenance coatings that have lower levels of photoactivitythan self-cleaning coatings and yet stay cleaner than uncoated glass,are easier to clean than uncoated glass, or both.

Anti-static coatings have been developed as one type of low-maintenancecoating. These coatings are often based on a transparent conductiveoxide (“TCO”) coating. The TCO coating typically has considerablethickness, and a relatively high level of electrical conductivity. Thethickness tends to be large enough that the coating imparts more than anoptimal amount of visible reflection, absorption and surface roughness.

It would be desirable to provide a low-maintenance coating thatcomprises titania and has a small thickness, minimal optical impact, andis static dissipative so as to provide controlled dust collectionproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken-away schematic cross-sectional view of a substratehaving a major surface with a static-dissipative coating in accordancewith certain embodiments;

FIG. 2 is a broken-away schematic cross-sectional view of a substratehaving a major surface with a static-dissipative coating in accordancewith other embodiments;

FIG. 3 is a broken-away schematic cross-sectional view of a substratehaving a first major surface with a static-dissipative coating and asecond major surface with a functional coating in accordance withcertain embodiments;

FIG. 4 is a partially broken-away schematic cross-sectional side view ofa multiple-pane insulating glazing unit that includes an interior panehaving a room-side surface with a static-dissipative coating inaccordance with certain embodiments;

FIG. 5 is a partially broken-away schematic cross-sectional side view ofa multiple-pane insulating glazing unit that includes an interior panehaving a room-side surface with a static-dissipative coating inaccordance with other embodiments; and

FIG. 6 is a schematic cross-sectional side view of a sputtering chamberused to deposit a static-dissipative coating in accordance with certainembodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is to be read with reference to thedrawings, in which like elements in different drawings have likereference numerals. The drawings, which are not necessarily to scale,depict selected embodiments and are not intended to limit the scope ofthe invention. Skilled artisans will recognize that the examplesprovided herein have many useful alternatives that fall within the scopeof the invention.

The invention provides a coated substrate. A wide variety of substratetypes are suitable for use in the invention. In some embodiments, thesubstrate 10′ is a sheet-like substrate having generally opposed first16 and second 18 major surfaces. For example, the substrate 10′ can be asheet of transparent material (i.e., a transparent sheet). The substrate10′, however, is not required to be a sheet, nor is it required to betransparent.

For many applications, the substrate 10, 10′ will comprise a transparent(or at least translucent) material, such as glass or clear plastic. Forexample, the substrate 10, 10′ is a glass sheet (e.g., a window pane) incertain embodiments. A variety of known glass types can be used, andsoda-lime glass will commonly be preferred. In certain preferredembodiments, the substrate 10, 10′ is part of a window, skylight, door,shower door, or other glazing. In some cases, the substrate 10, 10′ ispart of an automobile windshield, an automobile side window, an exterioror interior rear-view mirror, or a roof panel. In other embodiments, thesubstrate 10, 10′ is a piece of aquarium glass, a plastic aquariumwindow, or a piece of greenhouse glass. In a further embodiment, thesubstrate 10, 10′ is a refrigerator panel, such as part of arefrigerator door or window. In still another embodiment, the substrate10, 10′ is part of an oven door or window. In yet another embodiment,the substrate 10, 10′ is part of a switchable smart window, such as aswitchable privacy window.

Substrates of various sizes can be used in the present invention.Commonly, large-area substrates are used. Certain embodiments involve asubstrate 10, 10′ having a major dimension (e.g., a length or width) ofat least about 0.5 meter, preferably at least about 1 meter, perhapsmore preferably at least about 1.5 meters (e.g., between about 2 metersand about 4 meters), and in some cases at least about 3 meters. In someembodiments, the substrate 10′ is a jumbo glass sheet having a lengthand/or width that is between about 3 meters and about 10 meters, e.g., aglass sheet having a width of about 3.5 meters and a length of about 6.5meters. Substrates having a length and/or width of greater than about 10meters are also anticipated.

In some embodiments, the substrate 10, 10′ is a generally square orrectangular glass sheet. The substrate in these embodiments can have anyof the dimensions described in the preceding paragraph and/or in thefollowing paragraph. In one particular embodiment, the substrate 10, 10′is a generally rectangular glass sheet having a width of between about 3meters and about 5 meters, such as about 3.5 meters, and a length ofbetween about 6 meters and about 10 meters, such as about 6.5 meters. Inanother embodiment, the substrate 10, 10′ is a generally square glasssheet having a width of between about 4 inches and 8 inches, such asabout 6 inches.

Substrates of various thicknesses can be used in the present invention.In some embodiments, the substrate 10, 10′ (which can optionally be aglass sheet) has a thickness of about 1-5 mm. Certain embodimentsinvolve a substrate 10, 10′ with a thickness of between about 2.3 mm andabout 4.8 mm, and perhaps more preferably between about 2.5 mm and about4.8 mm. In one particular embodiment, a sheet of glass (e.g., soda-limeglass) with a thickness of about 3 mm is used. In one group ofembodiments, the thickness of the substrate is between about 4 mm andabout 20 mm or perhaps between about 2 mm and about 19 mm. Thicknessesin this range, for example, may be useful for aquarium tanks (in whichcase, the substrate can optionally be glass or acrylic). When thesubstrate is float glass, it will commonly have a thickness of betweenabout 4 mm and about 19 mm. In another group of embodiments, thesubstrate 10, 10′ is a thin sheet having a thickness of between about0.35 mm and about 1.9 mm. Embodiments of this nature can optionallyinvolve the substrate 10, 10′ being a sheet of display glass or thelike.

The invention provides a substrate 10, 10′ bearing a static-dissipativecoating 50. The static-dissipative coating 50 includes a film 30comprising titanium oxide (i.e., “titania”). Preferably, the film 30comprising titania defines an outermost, exposed face of thestatic-dissipative coating 50. Reference is made to FIGS. 1 and 2.

The static-dissipative coating 50 provides the substrate 10, 10′ with acombination of desirable optical properties and surprisinglow-maintenance properties. For example, it has a small thickness,minimal optical impact, and is static dissipative so as to providecontrolled dust collection properties.

The present coating stays cleaner longer than uncoated glass, is easierto clean than uncoated glass, or both. Although the coating 50 mayexhibit a level of photoactivity when activated by ultravioletradiation, it does not rely on ultraviolet activation, or photocatalysisof organics, to provide low-maintenance properties. It is therefore wellsuited for indoor (e.g., room-side) applications.

The static-dissipative coating 50 preferably provides the substrate 10,10′ with an indoor dust collection factor of less than 0.145. Inpreferred embodiments, the indoor dust collection factor is less than0.142 but greater than 0.050, for example less than 0.140 but greaterthan 0.050. In some embodiments, the indoor dust collection factor isless than 0.128 but greater than 0.050. The indoor dust collectionfactor reflects the extent to which the coated surface collects dustunder defined conditions that have been established to approximatecommon indoor air movement conditions.

Specifically, the indoor dust collection factor is the dust collected ingrams for a given sample as calculated in accordance with the Glass DustHazing test method specified in the IBR JN 16775 Protocol, the contentsof which are incorporated herein by reference. The purpose of the testis to determine the amount of dust that adheres to a glass surfaceoriented parallel to air flow. Dust-laden air is swept over the samples.The test is conducted using an air velocity of 1.1 miles/hour (100feet/minute); a calibrated air flow meter is used. The duct size is 24inches by 24 inches (stainless steel ducting), and the glass sample sizeis four inches by four inches. Each glass sample is tested with itscoated side facing up. A dust aerosol generator capable of 10 to 50 mgdust per m³ of air is used. The challenge aerosol is ISO 12103-1 A2 FineDust (silica dust); a dust concentration of 50 mg/m³ is used. A suitablephotometer for measuring dust concentration is the Thermo Electron ModelDR-2000. The dust is neutralized using an ion generator to simulatenatural conditions. The test area cleaning and setup involves wipingdown the ducting with moistened wipes, and purging with HEPA filteredair. The test protocol is as follows. Turn on air flow, and set to thedesired rate. Mount a cleaned glass sample in the duct with its coatedmajor surface parallel to the air flow and two inches above the ductbase. Inject ISO silica dust to the desired concentration. Neutralizethe dust at the generator exit. Monitor dust concentration duringexposure with the photometer. Conduct flow for 30 minutes using astopwatch. Stop the flow. Wipe the test glass with a pre-weighed tackcloth (e.g., HDX Tack Cloth). Weigh the same tack clock after suchwiping. An analytical balance accurate to 0.001 g, with span to 60 g, isused to determine the weight difference for the tack cloth, so as todetermine the change in weight due to the dust that had accumulated onthe coated glass surface and that was subsequently transferred to thetack cloth. The resulting dust collected by the sample (in grams) is theindoor dust collection factor.

In some embodiments, the static-dissipative coating 50 is on a surfaceof a substrate 10′ mounted such that the coating is exposed to an indoor(e.g., room-side) environment, e.g., so as to be exposed to an ambientenvironment inside a building. Certain embodiments provide an IG unithaving the static-dissipative coating 50 on an exterior surface (e.g., a#4 or #6 surface) that is destined to be exposed to an indoorenvironment.

While the present coating is particularly advantageous for indoorapplications, it also offers advantages for use as a #1 surface coating(i.e., a coating on a surface destined to be exposed to an outdoorenvironment). For example, the static-dissipative coating 50 preferablyprovides the substrate 10, 10′ with an outdoor dust collection factor ofless than 0.036, for example less than 0.035. In preferred embodiments,the outdoor dust collection factor is less than 0.032 but greater than0.010, for example less than 0.030 but greater than 0.010. In someembodiments, the outdoor dust collection factor is less than 0.028 butgreater than 0.010. The outdoor dust collection factor reflects theextent to which the coated substrate collects dust under definedconditions that have been established to approximate common outdoor airmovement conditions.

As with the indoor dust collection factor, the outdoor dust collectionfactor is the dust collected in grams for a given sample as calculatedin accordance with the Glass Dust Hazing test method specified in theabove-noted IBR JN 16775 Protocol. Here again, the purpose of the testis to determine the amount of dust that adheres to a glass surfaceoriented parallel to air flow when dust-laden air is swept over thesamples. Measurement of the outdoor dust collection factor is conductedusing an air velocity of 10.0 miles/hour (880 feet/minute) and a ductsize of 12 inches by 12 inches (stainless steel ducting). The glasssample size is four inches by four inches, each glass sample is testedwith its coated side facing up, a calibrated air flow meter is used, adust aerosol generator capable of 10 to 50 mg dust per m³ of air isused, the challenge aerosol is ISO 12103-1 A2 Fine Dust, a dustconcentration of 50 mg/m³ is used, and a suitable photometer formeasuring dust concentration is the Thermo Electron Model DR-2000. Thedust is neutralized using an ion generator to simulate naturalconditions. The test area cleaning and setup involves wiping down theducting with moistened wipes, and purging with HEPA filtered air. Aswith the indoor dust collection factor, the test protocol for theoutdoor dust collection factor is as follows. Turn on air flow, and setto the desired rate. Mount a cleaned glass sample in the duct with itscoated major surface parallel to the air flow and two inches above theduct base. Inject ISO silica dust to the desired concentration.Neutralize the dust at the generator exit. Monitor dust concentrationduring exposure with the photometer. Conduct flow for 30 minutes using astopwatch. Stop the flow. Wipe the test glass with a pre-weighed tackcloth. Weigh the same tack clock after such wiping. An analyticalbalance accurate to 0.001 g, with span to 60 g, is used to determine theweight difference for the tack cloth, so as to determine the change inweight due to the dust that had accumulated on the coated glass surfaceand that was subsequently transferred to the tack cloth. The resultingdust collected by the sample (in grams) is the outdoor dust collectionfactor.

Thus, in some embodiments, the static-dissipative coating is on a #1surface of a substrate 10 mounted such that the coating is exposed to anoutdoor environment, e.g., so as to exposed to periodic contact withrain. Certain embodiments provide an IG unit having thestatic-dissipative coating 50 on an exterior surface (i.e., a #1surface) that is destined to be exposed to an outdoor environment. Suchan embodiment is shown in FIG. 5.

The static-dissipative coating 50 of any embodiment of the presentdisclosure can optionally provide the substrate with a surface roughnessR_(a) in the range of between about 0.05 nm and about 5 nm, such asbetween 0.2 nm and 4 nm. Surface roughness is defined in terms ofdeviations from the mean surface level. In certain embodiments, thesurface roughness is less than 0.25, or even less than 0.22, such asfrom 0.05 to 0.20. The surface roughness R_(a) is the arithmetical meansurface roughness. This is the arithmetic average of the absolutedeviations from the mean surface level. The arithmetical mean surfaceroughness of a coating is commonly represented by the equation:R_(a)1/L∫₀ ^(L)|f(x)|dx. The surface roughness R_(a) can be measured inconventional fashion, e.g., using an Atomic Force Microscope (AFM)equipped with conventional software that gives R_(a).

In addition to having a surface roughness in one or more of the rangesnoted in the preceding paragraph, the static-dissipative coating 50preferably provides the substrate 10, 10′ with a wet dynamic coefficientof friction of less than 0.1, less than 0.075, or even less than 0.07.In some embodiments, the wet dynamic coefficient of friction of thecoated surface is in the range of from about 0.01 to about 0.065, suchas about 0.05. The wet dynamic coefficient of friction is measured asfollows. The coated glass sample is placed horizontally in a testinstrument (Mecmesin Multitest 2.5-i), covered with Windex, and a 2.5ounce test puck is placed on top of the sample. The bottom of the puckhas a piece of crock cloth on it in contact with the coated samplesurface (the crock cloth is an ISO standard material commerciallyavailable from Testfabrics, Inc., of West Pittston, Pa. USA). The puckis drawn across the coated surface, and the force required to do so ismeasured. As the puck is moving, the force is constant. This frictionforce is compared to the downward (gravitational) force of the puck todetermine a coefficient of (wet) dynamic friction. The numbers reportedherein are for fresh glass with the film 30 comprising titania in anun-activated-by-UV state.

The static-dissipative coating 50 preferably has a total thickness ofless than 500 angstroms, or less than 350 angstroms, such as greaterthan 30 angstroms and less than 300 angstroms. In some cases, thethickness of the static-dissipative coating 50 is less than 250angstroms, or even less than 200 angstroms, such as greater than 25angstroms and less than 200 angstroms. In one embodiment, the thicknessof the static-dissipative coating 50 is about 60 angstroms. In anotherembodiment, the thickness of the static-dissipative coating 50 is about160 angstroms.

FIG. 1 shows a substrate 10′ with a major surface 18 bearing astatic-dissipative coating 50 according to one embodiment. In somecases, the static-dissipative coating 50 includes one or more otherfilms beneath the film 30 comprising titania. In other cases, thestatic-dissipative coating 50 has only a single film 30, which isdirectly on (i.e., in contact with) the substrate 10′. In such cases,the static-dissipative coating 50 consists of the film 30 comprisingtitania.

FIG. 2 shows a substrate 10′ with a major surface 18 bearing astatic-dissipative coating 50 according to another embodiment. In FIG.2, the static-dissipative coating 50 includes both the film 30comprising titania and a base film 20. In some cases, thestatic-dissipative coating 50 further includes one or more other filmsbeneath the film 30 comprising titania. For example, one or more otherfilms can be provided beneath the base film 20, between the base film 20and the film 30 comprising titania, or both. In other cases, thestatic-dissipative coating 50 consists essentially of, or consists of,the base film 20 and the film 30 comprising titania.

The present coating 50 preferably has a level of electricalconductivity. However, even for embodiments where this is the case, thesurface resistance of the coating 50 is relatively large. For example,the surface resistance preferred for the static-dissipative coating 50is well above the typical range reported for anti-static coatings, whichis 10° 40³ ohm/square. By comparison, the present static-dissipativecoating 50 preferably has a surface resistance of greater than 10⁶ ohmsper square. In some cases, the surface resistance is greater than 10⁶ohms per square but less than 10¹¹ ohms per square. In certain preferredembodiments, the surface resistance is greater than 10⁸ ohms per squarebut less than 10¹¹ ohms per square. Surface resistance can be measuredin standard fashion using a surface resistivity meter. The noted surfaceresistance numbers reflect measurements taken at room temperature and30% relative humidity.

The static-dissipative coating 50 preferably is devoid of a transparentconductive oxide layer (e.g., a layer formed of ITO, FTO, AZO, or anyother electrically conductive oxide material) beneath the film 30comprising titania. In any embodiment of the present disclosure, thestatic-dissipative coating 50 can optionally be devoid of anyelectrically conductive film (e.g., a layer formed of metal or TCO)beneath the film 30 comprising titania. In such cases, if desired atransparent conductive oxide layer or another electrically conductivefilm can still be provided on an opposite side of the substrate.

In some embodiments, the film 30 comprising titania includes TiO₂, TiO,or both. In some cases, the film 30 comprising titania consistsessentially of (or consists of) titanium oxide. In such cases, the filmcomprising titania is devoid of any additional material, such as adopant. In other cases, the film 30 comprising titania further includesa dopant. The optional dopant material can generally be present in anamount of up to ten atomic percent, e.g., about five atomic percent orless. As one example, the film 30 comprising titania can also includetungsten.

The film 30 comprising titania can be doped with a material, and to alevel, that provide an electrical conductivity within one or more of theranges noted above. In embodiments of this nature, the film 30comprising titania preferably is doped with a material, and to a level,that provide the particular indoor and/or outdoor dust collectionfactors noted above. The dopant can be tungsten, niobium, silver,zirconium, tantalum, sodium, aluminum, zinc, chromium, vanadium,nitrogen, manganese, molybdenum, iron, nickel, calcium carbon, sulfur,boron, phosphorous, fluorine, or iodine, or mixtures or compound ofthese elements.

Additionally or alternatively, to provide a level of electricalconductivity, the film 30 comprising titania can includesubstoichiometric titanium oxide, i.e., TiO_(x), where x is less than 2.The suboxide composition can be chosen to help provide an electricalconductivity within one or more of the ranges noted above. Inembodiments of this nature, the suboxide composition preferably ischosen to help provide the particular indoor and/or outdoor dustcollection factors noted above. In some cases, the film 30 consistsessentially of (or consists of) TiO_(x), where x is less than 2. Forexample, the film 30 can optionally consist essentially of (or consistof) TiO_(x), where x is less than 2 but greater than 1.8. In thesecases, the TiO is devoid of an additional material such as a dopant.

In other cases, the film 30 comprising titania includes both tungsten(or another dopant selected from the list above) and TiO_(x), where x isless than 2. For example, the film 30 comprising titania can optionallyinclude both tungsten (or another dopant selected from the list above)and TiO_(x), where x is less than 2 but greater than 1.8.

The film 30 comprising titania can be a homogenous film, a graded film,or another type of non-homogenous film. The thickness of the film 30comprising titania preferably is less than 500 Å, such as greater than30 angstroms and less than 300 angstroms. In some embodiments, thethickness of the film 30 comprising titania is less than 250 Å, such asless than 200 Å, less than 150 Å, or even less than 100 Å. The thicknessof the film 30 comprising titania is greater than 25 Å, and preferably30 Å or greater, such as in the range of 30-95 Å. In certainembodiments, the film 30 consists of titania (or titania doped with oneor more of the materials noted above) at a thickness of 30-75 Å, such asabout 60 Å. In some of these embodiments, the titania is substoichiometric titanium oxide.

When provided, the base film 20 can be any suitable thin film materialthat adheres well to both the substrate 10, 10′ and the immediatelyoverlying film (which may be the film 30 comprising titania). In caseswhere the substrate 10, 10′ is soda-lime glass, the base film 20preferably also protects the film 30 comprising titania from sodium iondiffusion. In cases where the base film 20 is omitted and the substrate10, 10′ is soda-lime glass, the surface of the substrate itself canoptionally be treated to reduce, or perhaps deplete, the sodium ions inthe surface area of the glass.

The base film 20 can be a transparent dielectric film. In certainembodiments, the base film comprises silica, alumina, or both. The basefilm 20 can optionally be a mixed film including two or more metals orsemi-metals. In some cases, it is a mixed film comprising silica andalumina, or silica and titania, or silica, alumina and titania. Othermaterials can be used instead. In some embodiments, the base filmconsists essentially of (or consists of) silica, or consists essentially(or consists of) of alumina. In other embodiments, the base filmconsists essentially of (or consists of) silicon nitride, or consistsessentially (or consists of) of silicon oxynitride. The base film 20 canbe a substantially homogenous film or a graded film. When provided, thebase film 20 can be deposited directly onto the substrate, with the film30 comprising titania deposited directly onto the base film 20. This,however, is by no means required.

When provided, the base film 20 can optionally have a thickness of lessthan about 300 Å. In certain embodiments, the base film 20 has athickness of less than 150 Å. As one example, the base film 20 cancomprise silica at a thickness of about 100 Å.

In certain embodiments, the static-dissipative coating 50 is provided onone major surface of a substrate 10, 10′ and another functional coating80 is provided on an opposite major surface of the same substrate. FIG.3 shows one such embodiment. Here, the illustrated substrate 10′ has onesurface 18 bearing the static-dissipative coating 50 and another surface16 bearing another functional coating 80. Functional coating 80 can be asingle layer or a stack of layers. Various functional coatings can beused. For example, functional coating 80 can optionally be alow-emissivity coating comprising one or more infrared-reflectivemetallic films. Such metallic film(s) commonly comprise (e.g., areformed of) silver. Suitable low-emissivity coatings are described inU.S. Pat. Nos. 9,376,853 and 7,192,648 and 7,060,359 and 7,101,810, thecontents of which are incorporated herein by reference. When provided,functional coating 80 can alternatively be a transparent conductiveoxide coating, i.e., a coating comprising at least one transparentconductive oxide layer, such as ITO, FTO, AZO, or the like. Suitabletransparent conductive oxide coatings are described in U.S. Pat. No.9,453,365, the contents of which are incorporated herein by reference.

In the embodiment of FIG. 4, substrate 10′ is a transparent pane (e.g.,a glass sheet) that is part of a multiple-pane insulating glazing unit110. Typically, the insulating glazing unit 110 has an exterior pane 10and an interior pane 10′ separated by at least one between-pane space800. At least one spacer 900 (which can optionally be part of a sash) iscommonly provided to separate the panes 10 and 10′. The spacer 900 canbe secured to the interior surfaces of each pane using an adhesive orseal 700. In some cases, an end sealant 600 is also provided. In theillustrated embodiment, the exterior pane 10 has an exterior surface 12(the #1 surface) and an interior surface 14 (the #2 surface). Theinterior pane 10′ has an interior surface 16 (shown as a #3 surface) andan exterior surface 18 (shown as a #4 surface), which is the room-sidesurface. The IG unit can optionally be mounted in a frame (e.g., awindow frame) such that the exterior surface 12 of the exterior pane 10is exposed to an outdoor environment 77 while the exterior surface 18 ofthe interior pane 10′ is exposed to a room-side interior environment.Interior surfaces 14 and 16 are both exposed to the atmosphere in thebetween-pane space 800 of the insulating glazing unit. While FIG. 4shows a double-pane IG unit, other embodiments provide a triple-pane IGunit having the static-dissipative coating 50 on the #6 surface, the #1surface, or both.

The IG unit 110 can be filled with a conventional insulative gas mix(e.g., argon and air), or it can be a vacuum IG unit. In otherembodiments, it is a switchable smart glazing, such as a privacy glazingswitchable between transparent and opaque states.

When it is desired to provide a room-side surface of a window or otherglazing with low-maintenance properties, the static-dissipative coating50 can be provided quite advantageously. Thus, in the embodiment of FIG.4, the exterior surface 18 of pane 10′ has the static-dissipativecoating 50. The static-dissipative coating 50 shown in FIG. 4 can be inaccordance with any embodiment of the present disclosure. Of course,skilled artisans would understand that the static-dissipative coating 50can be provided on the exterior surface 12 of pane 10 in otherembodiments, as illustrated in FIG. 5.

With continued reference to FIG. 4, it is to be appreciated that theinterior surface 14 of pane 10 can optionally have a functional coating,such as a low-emissivity coating. Additionally or alternatively, theinterior surface 16 of pane 10′ can optionally have a functionalcoating, such as a low-emissivity coating or a transparent conductivecoating. Moreover, while FIG. 4 shows a double-pane IG unit, it canalternatively have three or more panes. Further, the static-dissipativecoating 50 can additionally or alternatively be provided on the #1surface of the IG unit 110.

Methods for producing a substrate 10, 10′ bearing a static-dissipativecoating 50 are also provided. In such methods, each film of the coating50 can be deposited using any of a variety of well-known coatingtechniques. Suitable coating techniques include, but are not limited to,sputter deposition, chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition, pyrolytic deposition, sol-gel deposition, andwet chemical deposition. In preferred embodiments, the coating 50 isdeposited by sputtering. Sputtering is well known in the present art.

FIG. 6 schematically depicts an exemplary magnetron sputtering chamber200 that can be used to deposit a static-dissipative coating 50.Magnetron sputtering chambers and related equipment are commerciallyavailable from a variety of sources (e.g., Leybold). Useful magnetronsputtering techniques and equipment are described in U.S. Pat. No.4,166,018, issued to Chapin, the teachings of which are incorporatedherein by reference. The sputtering chamber 200 shown in FIG. 6 includesa base (or “floor”) 220, a plurality of side walls 222, and a ceiling(or “top lid” or “cover”) 230, together bounding a sputtering cavity202. In FIG. 6, two upper targets 280 a, 280 b are shown mounted abovethe path of substrate travel 45. The substrate 10′ is conveyed along thepath of substrate travel 45 during film deposition, optionally over aplurality of spaced-apart transport rollers 210. In FIG. 6, two uppertargets are provided in the illustrated sputtering chamber, althoughthis is by no means required. For example, a single sputtering target(cylindrical or planar) can alternatively be provided in the sputteringchamber. As another possibility, the target(s) could be lower targetspositioned below the path of substrate travel and adapted for upwardlysputter depositing the static-dissipative coating 50 onto a bottomsurface of the substrate.

In certain embodiments, a method of depositing a static-dissipativecoating 50 is provided. The method includes depositing the film 30comprising titania onto a major surface of a substrate. The sputteringchamber of FIG. 6 can be used to deposit the film 30. Thus, targets 280a, 280 b can be titanium-containing targets. In some cases, thetitanium-containing targets 280 a, 280 b have a sputterable materialthat consists of metallic titanium. In other cases, thetitanium-containing targets 280 a, 280 b have a sputterable materialthat includes both metallic titianium and a metallic dopant, such astungsten. In still other cases, the targets have a sputterable materialcomprising substoichiometric titanium oxide, and the sputtering iscarried out in an inert gas atmosphere or a gas atmosphere with littleor no oxygen.

As noted above, the film 30 can in some cases comprise substoichiometricTiO_(x), where x is less than 2. In such cases, a sputtering chamber asshown in FIG. 6 can be used, and the targets 280 a, 280 b can each havea sputterable material comprising titanium. For example, the targetseach have a sputterable material comprising substoichiometric titaniumoxide, and an inert (or weakly oxygen) atmosphere can be used in thechamber. In such cases, different levels of oxygen can be used in thesputtering chamber. More will be said of this later. In other cases, thetargets 280 a, 280 b each have a sputterable material consisting ofmetal titanium, and an oxygen-containing atmosphere is used forsputter-depositing the film 30.

In some embodiments, the targets 280 a and 280 b each have atitanium-containing sputterable material, and they are sputtered underconditions selected to deposit a film 30 comprising substoichiometricTiO_(x), where x is less than 2. This may involve sputtering in an inertgas atmosphere or a gas atmosphere with little or no oxygen. Metallictitanium targets, for example, can be sputtered in an atmospherecomprising between 10% to 35% argon with the remainder being oxygen(e.g., in an atmosphere comprising between 15% to 25% argon with theremainder being oxygen, or perhaps in an atmosphere comprising between17% to 23% argon with the remainder being oxygen, such as about 20%argon with the remainder being oxygen).

In certain embodiments, the sputterable material consists essentially oftitanium metal and tungsten metal. For example, an alloy targetcomprising both titanium and tungsten can be used. Alternatively, onecould use a metal titanium target provided with strips (or the like) ofmetal tungsten. Another possibility is a metal alloy target withtungsten metal strips attached. When metal targets are sputtered, anoxygen atmosphere (optionally with a small amount of nitrogen) can beused. In other cases, the sputterable material comprises both titaniumoxide and tungsten oxide. In these cases, an inert atmosphere or slightoxygen atmosphere (optionally with a small amount of nitrogen) can beused. In certain embodiments, the sputterable material comprisestitanium monoxide, titanium dioxide, and tungsten oxide. In theseembodiments, a weakly oxygen atmosphere (optionally containing a smallamount of nitrogen) can be used. Or, the targets could be sputtered inan inert atmosphere, e.g., if the resulting film is not required to bedeposited in fully oxidized form. In certain cases, the sputterablematerial is characterized by a metal-only atomic ratio of between about0.01 and 0.34, this ratio being the number of tungsten atoms in thesputterable material divided by the number of titanium atoms in thesputterable material.

A target with sputterable material comprising both titanium and tungstencan be prepared using a number of different methods. In someembodiments, a target is prepared by plasma spraying titanium oxidetogether with tungsten metal onto a target base in an atmosphere that isoxygen deficient and does not contain oxygen-containing compounds.During the plasma spraying process, the action of the plasma on thetitanium oxide causes the titanium oxide to lose some oxygen atoms fromtheir lattices. These oxygen atoms are believed to combine with themetal tungsten to form tungsten oxide, as tungsten has a highelectrochemical potential. The titanium oxide sprayed onto the backingtube may thus comprise titanium monoxide, titanium dioxide, and tungstenoxide. The sputterable target may, as just one example, be a cylindricalrotary target having a backing tube with a length of at least 24 inches.In such cases, the sputterable material is carried on an exterior wallof the backing tube. Such a cylindrical target is adapted to rotateabout a central axis to which the exterior wall of the backing tube issubstantially parallel. Alternatively, hot isostatic pressing may beused to form a target. Other target forming methods can also be used.Suitable targets are also commercially available, from a number ofwell-known suppliers, such as Soleras Advanced Coatings BVBA, of Deinze,Belgium.

When the film 30 comprising titania is deposited by sputtering one ormore targets comprising substoichiometric TiO_(x), the sputtering ispreferably carried out using argon, a mixture of argon and oxygen, amixture of nitrogen and argon, a mixture of nitrogen and oxygen, or amixture of oxygen, nitrogen, and argon. If the plasma gas does notcontain oxygen, e.g., if pure argon is used, then the coating will notbe fully oxidized when deposited. In contrast, if the plasma gascontains oxygen, then the reduced form(s) of titanium oxide may beconverted during the sputtering process into the transparent form, whichis stoichiometric or at least substantially stoichiometric. A filmcomprising titania and tungsten oxide can be produced in this way. Thedegree of transparency of the film will depend upon the amount of oxygenin the plasma gas. An exemplary gas mixture to form transparent film isabout 20% by volume argon and about 80% by volume of oxygen.

Example 1 (Control)

A coating consisting of 60 angstroms of TiO₂ was deposited onto a majorsurface of a soda-lime glass sheet. The coating was deposited by pulsedDC sputtering, at a power of 5 kW, a frequency of 50 kHz, a voltage of379, and an amperage of 13.19. Two passes of the substrate were madeunder a metallic titanium target. The conveyance speed was 29.43 inchesper minute. The following process parameters were used: 100% O₂ gas,flow rate of 610 sccm, and pressure of 4.5 mtorr. The surface resistanceof the resulting coating was about 3.5×10¹¹ ohms/square. The resultingfilm was deposited as fully stoichiometric TiO₂.

Example 2

A static-dissipative coating consisting of 62 angstroms ofsubstoichiometric titanium oxide (TiO_(x), where x is 1.8 or higher andless than 2) was deposited onto a major surface of a soda-lime glasssheet. The coating was deposited by pulsed DC sputtering, at a power of5 kW, a frequency of 50 kHz, a voltage of 371, and an amperage of 13.49.Two passes of the substrate were made under a metallic titanium target.The conveyance speed was 25.89 inches per minute. The following processparameters were used: 20% argon/80% O₂ gas mix, argon flow rate of 153sccm, oxygen flow rate of 438 sccm, and pressure of 4.5 mtorr. Thesurface resistance of the resulting coating was about 1.8×10¹⁰ohms/square.

Example 3

A static-dissipative coating consisting of 60 angstroms ofsubstoichiometric titanium oxide (TiO_(x) where x=1.8 or higher) wasdeposited onto a major surface of a soda-lime glass sheet. The coatingwas deposited by pulsed DC sputtering, at a power of 5 kW, a frequencyof 50 kHz, a voltage of 363, and an amperage of 13.79. Two passes of thesubstrate were made under a metallic titanium target. The conveyancespeed was 24.87 inches per minute. The following process parameters wereused: 50% argon/50% O₂ gas mix, argon flow rate of 305 sccm, oxygen flowrate of 305 sccm, and pressure of 4.5 mtorr. The surface resistance ofthe resulting coating was about 5.8×10⁹ ohms/square. The value x inExample 3 is lower than the value x in Example 2.

Results

In dust collection testing, Example 2 performed about 12% better thanExample 1, while Example 3 performed about 7% better than Example 1.Thus, both Example 2 and Example 3 exhibited better dust collectionproperties than Example 1 (Control). The surface resistance of Example 3was smaller than that of Example 2. Surprisingly, even though Example 3was more electrically conductive (and had a lower x value for theTiO_(x)) than in than Example 2, Example 2 exhibited better dustcollection properties than Example 3.

Thus, certain embodiments of the invention provide a static-dissipativecoating 50 that includes a film 30 comprising substoichiometric titaniumoxide film produced by sputtering in an atmosphere comprising a mix ofoxygen gas and inert gas (such as argon), where the sputtering gas mixcomprises about 10-35% inert gas (e.g., argon) and about 65-90% oxygengas, such as 15-25% inert gas (e.g., argon) and 75-85% oxygen gas. Thisparticular type of substoichiometric titanium oxide can be used as thefilm 30 comprising titania in any embodiment of the present disclosure.

While certain preferred embodiments of the invention have beendescribed, it should be understood that various changes, adaptations andmodifications can be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A transparent substrate on which there is provided astatic-dissipative coating, the static-dissipative coating including afilm comprising titania over a base film, the film comprising titaniabeing exposed so as to define an outermost face of thestatic-dissipative coating, the static-dissipative coating characterizedby an indoor dust collection factor of less than 0.145.
 2. Thetransparent substrate of claim 1 wherein the indoor dust collectionfactor is less than 0.142 but greater than 0.050.
 3. The transparentsubstrate of claim 2 wherein the indoor dust collection factor is lessthan 0.140 but greater than 0.050.
 4. The transparent substrate of claim1 wherein the static-dissipative coating is characterized by an outdoordust collection factor of less than 0.036.
 5. (canceled)
 6. Thetransparent substrate of claim 4 wherein the outdoor dust collectionfactor is less than 0.032 but greater than 0.010.
 7. The transparentsubstrate of claim 6 wherein the outdoor dust collection factor is lessthan 0.030 but greater than 0.010.
 8. The transparent substrate of claim1 wherein the static-dissipative coating has a surface resistance ofgreater than 10⁶ ohms per square.
 9. (canceled)
 10. The transparentsubstrate of claim 8 wherein the surface resistance of thestatic-dissipative coating is greater than 10⁸ ohms per square but lessthan 10¹¹ ohms per square.
 11. (canceled)
 12. The transparent substrateof claim 10 wherein the surface resistance of the static-dissipativecoating is greater than 3.0×10⁹ ohms per square but less than 7.0×10⁹ohms per square.
 13. (canceled)
 14. The transparent substrate of claim 1wherein the static-dissipative coating has a thickness that is greaterthan 30 angstroms and less than 300 angstroms. 15-16. (canceled)
 17. Thetransparent substrate of claim 1 wherein the static-dissipative coatingis devoid of an electrically conductive film beneath the film comprisingtitania.
 18. (canceled)
 19. The transparent substrate of claim 1 whereinthe film comprising titania comprises substoichiometric TiO_(x), where xis less than
 2. 20. The transparent substrate of claim 19 wherein thefilm comprising titania comprises substoichiometric TiO_(x), where x isless than 2 but greater than 1.8.
 21. The transparent substrate of claim20 wherein the substoichiometric TiO_(x) is a film produced bysputtering in an atmosphere comprising a mix of oxygen gas and inertgas, where the mix comprises about 10-35% inert gas and about 65-90%oxygen gas. 22-23. (canceled)
 24. The transparent substrate of claim 1wherein the static-dissipative coating has a wet dynamic coefficient offriction of less than 0.07.
 25. (canceled)
 26. An insulating glass unitcomprising two spaced-apart panes bounding a between-pane space, whereinone of the panes has an interior surface that is exposed to an interiorof a building and that bears a static-dissipative coating, thestatic-dissipative coating including a film comprising titania over abase film, the film comprising titania being exposed so as to define anoutermost face of the static-dissipative coating, the static-dissipativecoating characterized by an indoor dust collection factor of less than0.145.
 27. The insulating glass unit of claim 26 wherein the indoor dustcollection factor is less than 0.142 but greater than 0.050.
 28. Theinsulating glass unit of claim 27 wherein the indoor dust collectionfactor is less than 0.140 but greater than 0.050.
 29. The insulatingglass unit of claim 26 wherein the static-dissipative coating ischaracterized by an outdoor dust collection factor of less than 0.036.30. (canceled)
 31. The insulating glass unit of claim 29 wherein theoutdoor dust collection factor is less than 0.032 but greater than0.010.
 32. The insulating glass unit of claim 31 wherein the outdoordust collection factor is less than 0.030 but greater than 0.010. 33.The insulating glass unit of claim 26 wherein the static-dissipativecoating has a surface resistance of greater than 10⁶ ohms per square.34. The insulating glass unit of claim 33 wherein the surface resistanceof the static-dissipative coating is greater than 10⁸ ohms per squarebut less than 10¹¹ ohms per square.
 35. (canceled)
 36. The insulatingglass unit of claim 34 wherein the surface resistance of thestatic-dissipative coating is greater than 3.0×10⁹ ohms per square butless than 7.0×10⁹ ohms per square.
 37. (canceled)
 38. The insulatingglass unit of claim 26 wherein the static-dissipative coating has athickness that is greater than 30 angstroms and less than 300 angstroms.39-40. (canceled)
 41. The insulating glass unit of claim 26 wherein thestatic-dissipative coating is devoid of a conductive film beneath thefilm comprising titania.
 42. (canceled)
 43. The insulating glass unit ofclaim 26 wherein the film comprising titania comprises substoichiometricTiO_(x), where x is less than
 2. 44. The insulating glass unit of claim43 wherein the film comprising titania comprises substoichiometricTiO_(x), where x is less than 2 but greater than 1.8.
 45. The insulatingglass unit of claim 44 wherein the substoichiometric TiO_(x) is a filmproduced by sputtering in an atmosphere comprising a mix of oxygen gasand inert gas, where the mix comprises about 10-35% inert gas and about65-90% oxygen gas. 46-47. (canceled)
 48. The insulating glass unit ofclaim 26 wherein the static-dissipative coating has a wet dynamiccoefficient of friction of less than 0.07.
 49. (canceled)
 50. A glasssheet on which there is provided a static-dissipative coating, thestatic-dissipative coating including a film comprising titania, the filmcomprising titania being exposed so as to define an outermost face ofthe static-dissipative coating, and the film comprising titaniacomprises substoichiometric TiO_(x), where x is less than 2 but greaterthan 1.8, the substoichiometric TiO_(x) being a film produced bysputtering in an atmosphere comprising a mix of oxygen gas and inertgas, where the mix comprises about 10-35% inert gas and about 65-90%oxygen gas, the static-dissipative coating characterized by an indoordust collection factor of less than 0.145.